The Burlington Zephyr (later known as the Pioneer Zephyr) entered revenue service on November 11, 1934, on a route between Lincoln, Omaha, and Kansas City, and it remained on that route for most of its long life, being retired in 1960. It had a small baggage compartment, so conceivably this sticker was meant to be used on this train.
Of course, “zephyr” was the term Burlington applied to all of its streamlined trains, so this sticker might have been made for any of them. These stickers are pretty common, while I haven’t seen many, if any, specifically for, say, the Twin Zephyrs or Denver Zephyr, so it seems likely that these were used generically.
Here’s a slightly different version that mentions “streamlined” and “Diesel-powered” but not “built of stainless steel.” This may be from later when stainless-steel trains were common on many railroads.